1. Field of the Invention
This invention relates to coated abrasives, and, more particularly, to coated abrasive products containing erodable agglomerates.
2. Discussion of the Art
Conventional coated abrasives typically consist of a single layer of abrasive grain adhered to a backing. It has been found that only up to about 15% of the grains in the layer are actually utilized in removing any of the workpiece. It follows then that about 85% of the grains in the layer are wasted. Furthermore, the backing, one of the more expensive components of the coated abrasive, must also be disposed of before the end of its useful life.
To overcome this problem of waste, many attempts have been made to distribute the abrasive grains on the backing in such a manner so that a higher percentage of the abrasive grains can be utilized, thus leading to extended life of the coated abrasive product The extended life further leads to fewer belt or disc changes by the operators, thereby saving time and reducing labor costs. It is apparent that merely depositing a thick layer of abrasive grains on the backing will not solve the problem, because the grains lying below the topmost grains are not likely to be used.
A highly desirable abrasive grain is marketed under the trademark "Cubitron". "Cubitron" abrasive grain is a non-fused synthetic alumina-based mineral optionally containing certain metal oxide or spinel or both additives. "Cubitron" abrasive grain is described in U.S. Pat. Nos. 4,314,827; 4,744,802; 4,770,671; and 4,881,951.
Although "Cubitron" grain provides excellent performance, it is much more expensive than conventional aluminum oxide grain. It has long been known that a coated abrasive containing an underlayer of conventional aluminum oxide grains and a top layer of "Cubitron" grains provides satisfactory performance at a lower cost than a coated abrasive using 100% "Cubitron" grains. However, for certain grinding applications, the conventional abrasive grains prevent maximum utilization of the "Cubitron" grains that are randomly distributed between the conventional grains. If these conventional grains do not break down fast enough, they tend to compete with the "Cubitron" grains for contact with the metallic workpiece and rub rather than remove metal. This prevents the "Cubitron" grains from fully penetrating into the metal to allow them to remove large amounts of metal.